In recent years high-speed fluid and slurry jets have become a conventional tool in manufacturing, infrastructure maintenance and environment protection. A number of new non-traditional jet applications are emerging in mining, medicine and defense. These applications range from demolition of buildings and breakage of stones to eye surgery, from cleaning of the ocean bottom and deicing the roads to precision machining.
Conventionally the jets are formed by expelling a compressed fluid through an opening in a metal or ceramic body termed a nozzle. In most cases the openings are round. This geometry is determined by the conditions of the nozzle fabrication. It is much easier to generate a round opening in a solid body than an opening of any other geometry. The round nozzle minimizes the ratio between the surface and the flow rate of the stream. Thus it minimizes the specific head losses. The stability of the round jets that is its ability to resist decomposition into an array of droplets is maximal.
The round geometry has, however, significant shortcomings. In a number of practical cases a stream having high aspect ratio is more beneficial than the omni directional round stream. In the case of cutting the long side should be parallel to the direction of cutting (knife, saw), while in the case of cleaning the long side should be normal to the direction of the motion (brush). The enlargement of the length (cutting) or width (cleaning) of the jet cross section increases the rate of processing. But in the case of the omni directional round jet the increase of the useful dimension brings about unnecessary or even damaging change of the jet geometry. Increase of the width of a saw beyond the level, which assures its strength, results in the excessive energy consumption and material losses. Similarly, excessive diameter of the cutting jet brings about the needless losses of energy and material. Excessive jet diameter in the course of surface processing, similarly to an excessive width of a brush, increases energy consumption. Another shortcoming of the round jet is uneven rate of energy supply to the substrate by a moving jet. Thus, generation of the homogeneous surface in the course of the processing using the round jet is difficult if not impossible. Still another shortcoming of the round nozzles is impossibility to repair a worn nozzle. Because of this the highly erosive abrasive jets are conventionally formed by the entrainment of the abrasive particles by the jet rather than by the acceleration of the slurry.
The use of the shaped non-round (diamond, ellipse, etc.) openings improves nozzle performance. However due to the intensive wear these nozzles rapidly lose their integrity and thus cannot last sufficiently long. Besides, the formation of a precision shaped orifice in a hard solid material is an expensive operation.